1. Field of the Invention
The present invention relates to a signal processing technique for decoding a compression-encoded signal to an original signal, and to a technique for distributing a program used for decoding.
2. Related Art
In recent years, copyrighted articles such as music and movie films are recorded on optical disks such as DVDs and put to use.
An AV (Audio/Video) signal recorded on an optical disk has been compression-encoded so as to reserve a predetermined reproduction period within a limited memory capacity. Therefore, to reproduce the signal, decoding is needed to recover the original signal from the compression-encoded signal.
A conventional signal processing device for decoding a compression-encoded signal is explained below. The signal processing device includes a first input terminal, a second input terminal, a detecting unit, a procedure storing unit, a decoding unit, and an output terminal. The compression-encoded signal is input in the first input terminal, whereas a signal relating to an attribute of the compression-encoded signal, namely, a signal relating to a compression-encode format used for the compression-encoded signal, is input in the second input terminal. When the signal relating to the attribute is input in the second input terminal, the detecting unit specifies the compression-encode format used for the compression-encoded signal, and notifies the procedure storing unit of the compression-encode format. The procedure storing unit stores a plurality of decode procedures (programs) which each correspond to a different compression-encode format. When the compression-encoded signal is input in the first input terminal, the decoding unit decodes the compression-encoded signal in accordance with a decode procedure corresponding to the notified compression-encode format, to recover the original signal. The decoded signal is then output to an external device via the output terminal. Here, the procedure storing unit and the decoding unit are typically implemented on a single LSI decoder. Decode procedures corresponding to various compression-encode formats are stored in the procedure storing unit, and one of these decode procedures is selected based on the detection result by the detecting unit. The selected decode procedure is usually executed by software.
Recently, many different compression-encode formats have been employed to encode audio data, and as a result the variety of decode procedures (audio codecs) for decoding encoded audio data is on the increase. Examples of such decode procedures are AAC (Advanced Audio Compression), MP3 (MPEG Audio Layer 3), and WMA (Windows Media Audio). If all such audio codecs are stored in the procedure storing unit so as to support all available compression-encode formats, the circuit scale and cost of the decoder will increase. Besides, the user who buys the signal processing device may not need some of these audio codecs.